/******************************************************************************
 * Spine Runtimes License Agreement
 * Last updated January 1, 2020. Replaces all prior versions.
 *
 * Copyright (c) 2013-2020, Esoteric Software LLC
 *
 * Integration of the Spine Runtimes into software or otherwise creating
 * derivative works of the Spine Runtimes is permitted under the terms and
 * conditions of Section 2 of the Spine Editor License Agreement:
 * http://esotericsoftware.com/spine-editor-license
 *
 * Otherwise, it is permitted to integrate the Spine Runtimes into software
 * or otherwise create derivative works of the Spine Runtimes (collectively,
 * "Products"), provided that each user of the Products must obtain their own
 * Spine Editor license and redistribution of the Products in any form must
 * include this license and copyright notice.
 *
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 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
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 *****************************************************************************/

#ifdef SPINE_UE4
    #include "SpinePluginPrivatePCH.h"
#endif

#include <spine/Triangulator.h>

#include <spine/MathUtil.h>

using namespace spine;

Triangulator::~Triangulator() {
    ContainerUtil::cleanUpVectorOfPointers(_convexPolygons);
    ContainerUtil::cleanUpVectorOfPointers(_convexPolygonsIndices);
}

Vector<int> &Triangulator::triangulate(Vector<float> &vertices) {
    size_t vertexCount = vertices.size() >> 1;

    Vector<int> &indices = _indices;
    indices.clear();
    indices.ensureCapacity(vertexCount);
    indices.setSize(vertexCount, 0);
    for (size_t i = 0; i < vertexCount; ++i) {
        indices[i] = i;
    }

    Vector<bool> &isConcaveArray = _isConcaveArray;
    isConcaveArray.ensureCapacity(vertexCount);
    isConcaveArray.setSize(vertexCount, 0);
    for (size_t i = 0, n = vertexCount; i < n; ++i) {
        isConcaveArray[i] = isConcave(i, vertexCount, vertices, indices);
    }

    Vector<int> &triangles = _triangles;
    triangles.clear();
    triangles.ensureCapacity(MathUtil::max((int)0, (int)vertexCount - 2) << 2);

    while (vertexCount > 3) {
        // Find ear tip.
        size_t previous = vertexCount - 1, i = 0, next = 1;

        // outer:
        while (true) {
            if (!isConcaveArray[i]) {
                int p1 = indices[previous] << 1, p2 = indices[i] << 1, p3 = indices[next] << 1;
                float p1x = vertices[p1], p1y = vertices[p1 + 1];
                float p2x = vertices[p2], p2y = vertices[p2 + 1];
                float p3x = vertices[p3], p3y = vertices[p3 + 1];
                for (size_t ii = (next + 1) % vertexCount; ii != previous; ii = (ii + 1) % vertexCount) {
                    if (!isConcaveArray[ii]) continue;

                    int v = indices[ii] << 1;
                    float &vx = vertices[v], vy = vertices[v + 1];
                    if (positiveArea(p3x, p3y, p1x, p1y, vx, vy)) {
                        if (positiveArea(p1x, p1y, p2x, p2y, vx, vy)) {
                            if (positiveArea(p2x, p2y, p3x, p3y, vx, vy)) {
                                goto break_outer; // break outer;
                            }
                        }
                    }
                }
                break;
            }
        break_outer:

            if (next == 0) {
                do {
                    if (!isConcaveArray[i]) break;
                    i--;
                } while (i > 0);
                break;
            }

            previous = i;
            i = next;
            next = (next + 1) % vertexCount;
        }

        // Cut ear tip.
        triangles.add(indices[(vertexCount + i - 1) % vertexCount]);
        triangles.add(indices[i]);
        triangles.add(indices[(i + 1) % vertexCount]);
        indices.removeAt(i);
        isConcaveArray.removeAt(i);
        vertexCount--;

        int previousIndex = (vertexCount + i - 1) % vertexCount;
        int nextIndex = i == vertexCount ? 0 : i;
        isConcaveArray[previousIndex] = isConcave(previousIndex, vertexCount, vertices, indices);
        isConcaveArray[nextIndex] = isConcave(nextIndex, vertexCount, vertices, indices);
    }

    if (vertexCount == 3) {
        triangles.add(indices[2]);
        triangles.add(indices[0]);
        triangles.add(indices[1]);
    }

    return triangles;
}

Vector<Vector<float> *> &Triangulator::decompose(Vector<float> &vertices, Vector<int> &triangles) {
    Vector<Vector<float> *> &convexPolygons = _convexPolygons;
    for (size_t i = 0, n = convexPolygons.size(); i < n; ++i)
        _polygonPool.free(convexPolygons[i]);
    convexPolygons.clear();

    Vector<Vector<int> *> &convexPolygonsIndices = _convexPolygonsIndices;
    for (size_t i = 0, n = convexPolygonsIndices.size(); i < n; ++i)
        _polygonIndicesPool.free(convexPolygonsIndices[i]);
    convexPolygonsIndices.clear();

    Vector<int> *polygonIndices = _polygonIndicesPool.obtain();
    polygonIndices->clear();

    Vector<float> *polygon = _polygonPool.obtain();
    polygon->clear();

    // Merge subsequent triangles if they form a triangle fan.
    int fanBaseIndex = -1, lastwinding = 0;
    for (size_t i = 0, n = triangles.size(); i < n; i += 3) {
        int t1 = triangles[i] << 1, t2 = triangles[i + 1] << 1, t3 = triangles[i + 2] << 1;
        float x1 = vertices[t1], y1 = vertices[t1 + 1];
        float x2 = vertices[t2], y2 = vertices[t2 + 1];
        float x3 = vertices[t3], y3 = vertices[t3 + 1];

        // If the base of the last triangle is the same as this triangle, check if they form a convex polygon (triangle fan).
        bool merged = false;
        if (fanBaseIndex == t1) {
            size_t o = polygon->size() - 4;
            Vector<float> &p = *polygon;
            int winding1 = winding(p[o], p[o + 1], p[o + 2], p[o + 3], x3, y3);
            int winding2 = winding(x3, y3, p[0], p[1], p[2], p[3]);
            if (winding1 == lastwinding && winding2 == lastwinding) {
                polygon->add(x3);
                polygon->add(y3);
                polygonIndices->add(t3);
                merged = true;
            }
        }

        // Otherwise make this triangle the new base.
        if (!merged) {
            if (polygon->size() > 0) {
                convexPolygons.add(polygon);
                convexPolygonsIndices.add(polygonIndices);
            } else {
                _polygonPool.free(polygon);
                _polygonIndicesPool.free(polygonIndices);
            }

            polygon = _polygonPool.obtain();
            polygon->clear();
            polygon->add(x1);
            polygon->add(y1);
            polygon->add(x2);
            polygon->add(y2);
            polygon->add(x3);
            polygon->add(y3);
            polygonIndices = _polygonIndicesPool.obtain();
            polygonIndices->clear();
            polygonIndices->add(t1);
            polygonIndices->add(t2);
            polygonIndices->add(t3);
            lastwinding = winding(x1, y1, x2, y2, x3, y3);
            fanBaseIndex = t1;
        }
    }

    if (polygon->size() > 0) {
        convexPolygons.add(polygon);
        convexPolygonsIndices.add(polygonIndices);
    }

    // Go through the list of polygons and try to merge the remaining triangles with the found triangle fans.
    for (size_t i = 0, n = convexPolygons.size(); i < n; ++i) {
        polygonIndices = convexPolygonsIndices[i];

        if (polygonIndices->size() == 0) continue;
        int firstIndex = (*polygonIndices)[0];
        int lastIndex = (*polygonIndices)[polygonIndices->size() - 1];

        polygon = convexPolygons[i];
        size_t o = polygon->size() - 4;
        Vector<float> &p = *polygon;
        float prevPrevX = p[o], prevPrevY = p[o + 1];
        float prevX = p[o + 2], prevY = p[o + 3];
        float firstX = p[0], firstY = p[1];
        float secondX = p[2], secondY = p[3];
        int winding0 = winding(prevPrevX, prevPrevY, prevX, prevY, firstX, firstY);

        for (size_t ii = 0; ii < n; ++ii) {
            if (ii == i) continue;

            Vector<int> *otherIndicesP = convexPolygonsIndices[ii];
            Vector<int> &otherIndices = *otherIndicesP;

            if (otherIndices.size() != 3) continue;

            int otherFirstIndex = otherIndices[0];
            int otherSecondIndex = otherIndices[1];
            int otherLastIndex = otherIndices[2];

            Vector<float> *otherPolyP = convexPolygons[ii];
            Vector<float> &otherPoly = *otherPolyP;

            float x3 = otherPoly[otherPoly.size() - 2], y3 = otherPoly[otherPoly.size() - 1];

            if (otherFirstIndex != firstIndex || otherSecondIndex != lastIndex) continue;

            int winding1 = winding(prevPrevX, prevPrevY, prevX, prevY, x3, y3);
            int winding2 = winding(x3, y3, firstX, firstY, secondX, secondY);
            if (winding1 == winding0 && winding2 == winding0) {
                otherPoly.clear();
                otherIndices.clear();
                polygon->add(x3);
                polygon->add(y3);
                polygonIndices->add(otherLastIndex);
                prevPrevX = prevX;
                prevPrevY = prevY;
                prevX = x3;
                prevY = y3;
                ii = 0;
            }
        }
    }

    // Remove empty polygons that resulted from the merge step above.
    for (int i = (int)convexPolygons.size() - 1; i >= 0; --i) {
        polygon = convexPolygons[i];
        if (polygon->size() == 0) {
            convexPolygons.removeAt(i);
            _polygonPool.free(polygon);
            polygonIndices = convexPolygonsIndices[i];
            convexPolygonsIndices.removeAt(i);
            _polygonIndicesPool.free(polygonIndices);
        }
    }

    return convexPolygons;
}

bool Triangulator::isConcave(int index, int vertexCount, Vector<float> &vertices, Vector<int> &indices) {
    int previous = indices[(vertexCount + index - 1) % vertexCount] << 1;
    int current = indices[index] << 1;
    int next = indices[(index + 1) % vertexCount] << 1;

    return !positiveArea(vertices[previous], vertices[previous + 1],
                         vertices[current], vertices[current + 1],
                         vertices[next], vertices[next + 1]);
}

bool Triangulator::positiveArea(float p1x, float p1y, float p2x, float p2y, float p3x, float p3y) {
    return p1x * (p3y - p2y) + p2x * (p1y - p3y) + p3x * (p2y - p1y) >= 0;
}

int Triangulator::winding(float p1x, float p1y, float p2x, float p2y, float p3x, float p3y) {
    float px = p2x - p1x, py = p2y - p1y;
    return p3x * py - p3y * px + px * p1y - p1x * py >= 0 ? 1 : -1;
}
